1. Field of the Invention
The present invention relates to a process for making polyamine-epihalohydrin resin products having very low levels of residual epihalohydrin hydrolyzates with very high wet strength effectiveness.
2. Background and Material Information
Polyamine-epihalohydrin resins are cationic thermosetting materials used to increase the wet strength of papers. Often these materials contain large quantities of epihalohydrin hydrolysis products arising from the synthetic step (i.e., the reaction to produce the resin).
Commercial papermaking operations utilize paper wet strengthening formulations which comprise such cationic thermosetting polymers. In the papermaking process, waste material is frequently disposed of in landfills, etc. It is desirable to reduce the organohalogen content of such wastes to as low a level as possible. This waste is a substantially solid mass of material which is exposed to the environment. The exposure of the waste to the environment results in the selection of microorganisms which feed on the components in the waste. It is known that there are microorganisms which feed on the organohalogen compounds in the solid waste.
In the papermaking process the epichlorohydrin hydrolysis products arising from the synthetic step in the manufacture of polyamine-epichlorohydrin resins, are released into the environment in the water used to make paper, or into the air by evaporation during the paper drying step, or into the paper itself or a combination of these events. It is desirable to reduce and control these emissions into the environment to as low a level as possible.
Wet strength compositions which contain large quantities of epihalohydrin and/or epihalohydrin hydrolysis products display high wet strength effectiveness compared to similar products made using diminished or low quantities of epihalohydrin. Thus, there is a need to retain high wet strength effectiveness but also to reduce substantially the large quantities of undesirable halogenated by-products in the wet strength composition.
Several ways of reducing the quantities of epihalohydrin hydrolysis products have been devised. Reduction in the quantity of epihalohydrin used in the synthetic step is an alternative taught in U.S. Pat. No. 5,171,795. A longer reaction time results. Control over the manufacturing process is taught in U.S. Pat. No. 5,017,642 to yield compositions of reduced concentration of hydrolysis products.
Reduction in the amount of epihalohydrin used is effective in reducing epihalohydrin and epihalohydrin hydrolysis products in the wet strength composition but has the undesirable side effect of reducing wet strength performance in proportion to the reduction in epihalohydrin used. Therefore, conventional wisdom dictates that reduction in the amount of epihalohydrin employed in the polymerization reaction is to be avoided or else high wet strength effectiveness of such resins will be sacrificed.
Post-synthetic treatments may be used. U.S. Pat. No. 5,256,727 teaches that reacting the epihalohydrin and its hydrolysis products with dibasic phosphate salts or alkanolamines in equimolar proportions converts the chlorinated organic compounds into non-chlorinated species. To do this it is necessary to conduct a second reaction step for at least 3 hours, which adds significantly to costs and generates quantities of unwanted organic materials in the wet strength composition. In compositions containing large amounts of epihalohydrin and epihalohydrin hydrolysis products (e.g., about 1-6% by weight of the composition), the amount of organic material formed is likewise present in undesirably large amounts.
WO 92/22601 teaches that halogenated by-products can be removed from products containing high levels of halogenated by-products as well as low levels of halogenated by-products by the use of ion exchange resins. However, it is clear from the data presented that there are significant yield losses in wet strength composition and a reduction in wet strength effectiveness.
It is known that nitrogen-free organohalogen-containing compounds can be converted to a relatively harmless substance. For example, 1,3-dichloro-2-propanol, 1-chloro-2,3-propanediol, and epichlorohydrin have been treated with alkali to produce glycerol.
The conversion of nitrogen-free organohalogen compounds with microorganisms containing a dehalogenase is also known. For example, C. E. Castro, et al. ("Biological Cleavage of Carbon-Halogen Bonds Metabolism of 3-Bromopropanol by Pseudomonas sp.", Biochimica et Biophysica Acta, 100, 384-392, 1965) describe the use of Pseudomonas sp. isolated from soil that metabolizes 3-bromopropanol in sequence to 3-bromopropionic acid, 3-hydroxypropionic acid and CO.sub.2.
Various U.S. Patents also describe the use of microorganisms for dehalogenating halohydrins, e.g., U.S. Pat. Nos. 4,452,894; 4,477,570; and 4,493,895. Each of these patents is hereby incorporated by reference as though set forth in full herein.
EP-A-0 510 987 A1 teaches the use of microorganisms or enzymes derived from microorganisms to remove epihalohydrin and epihalohydrin hydrolysis products from wet strength compositions without reduction in wet strength effectiveness. Processes of removal are described which remove up to 2.6 weight per cent of halogenated by-product based on the weight of the composition. The amount of microorganism or enzyme used is in direct proportion to the quantity of halogenated by-product present. Thus, when present in large quantities (e.g., more than about 1% by weight of the composition) a large proportion of microorganism or enzyme is needed to adequately remove the unwanted product. Large quantities of halogenated byproduct can be toxic to the microbes employed in such dehalogenation processes. EP-A-0 510 987 A1 is a family member of U.S. patent application Ser. No. 08/243,492, filed May 16, 1994, now U.S. Pat. No. 5,470,742 which is both a continuation of U.S. patent application Ser. No. 07/866,216, filed Nov. 9, 1992, and a continuation-in-part of U.S. patent application Ser. No. 07/690,765, filed Apr. 9, 1992. Each of these documents is hereby incorporated by reference as though set forth in full herein.
It is also known that epihalohydrin and epihalohydrin hydrolyzates can be reacted with bases to form chloride ion and polyhydric alcohols. U.S. Pat. No. 4,975,499 teaches the use of bases during the synthetic step to reduce organo chlorine contents of wet strength composition to moderate levels (e.g., to moderate levels of from about 0.11 to about 0.16%) based on the weight of the composition. U.S. Pat. No. 5,019,606 teaches reacting wet strength compositions with an organic or inorganic base.
Each of the foregoing approaches has provided less than optimal results, and there has been a continuing need for improvement.